The present invention relates to an image display device in which the electron beam delivered from a substantially flat electron source is controlled and accelerated by electron beam control electrodes before being projected on the phosphor surface of the image display device, thereby forming the picture image display.
Heretofore, there has been developed matrix type flat plate shaped display devices in which EL, plasma, liquid crystals, etc., are used. In these devices, satisfactory performances are still not obtained with respect to the brightness, emission efficiency, color indication, etc., and such picture image display devices are still short of the quality needed for practical applications, e.g. for television.
On the other hand, an attempt at composing flat plate shaped display devices based on the use of an electron beam has been reported.
FIG. 1 shows the construction of the essential part of an example of display devices of this sort which have been known heretofore. Referring to this sketch, a flat plate shape electron source is provided which can be thermoionic cathodes, electric field discharge cold cathodes, etc., for example. A lattice shape electrode plate 2 having a large number of holes 6 therethrough is provided, on which voltage which is positive with respect to the flat plate shape electron source 1 is impressed to produce an electron beam. Part of the electron beam passes through the holes 6, and reaches the surface of a first electron beam control electrode plate 3. In the first electron beam control electrode plate 3 and a second electron beam control electrode plate 4, large number of holes 6a and 6b are provided and are regularly arranged longitudinally and laterally in rows and columns, and long strip shaped electrodes 7 and 8 are installed in an arrangement in which they criss-cross each other and with appropriate distance between them, and the holes 6a and 6b provided in the two electrodes at these intersections are in line with each other. The electron beam, as it reaches the surface of the first electron beam control electrode plate 3, has the current modulated corresponding to the signal voltage impressed on each electrode 7, while passing through the hole 6a, and then reaches the surface of the second electron beam control electrode plate 4.
At the second electron beam control electrode plate 4, the electron beam is modulated similar to that carried out at the first electron beam control electrode plate 3, as it passes through the hole 6b.
The electron beam which passed through the hole 6b is accelerated by an accelerating electrode plate 5 on which a high voltage is impressed, and impinges upon a phosphor film 9 coated on the surface of this accelerating electrode plate 5, causing it to emit light. Since the brightness of emission is proportional to the electron beam current on each picture element, a picture image corresponding to the signal voltage impressed on each of the electrodes installed on the two electron beam control electrode plates 3 and 4 can be produced. For the substrate 5 on which the accelerating electrode is mounted, a transparent insulating substrate, for example, glass, is employed, and on its surface, a transparent electrode is mounted, or a metal backing system like that of an ordinary cathode ray tube can be applied.
Generally, in display devices of this type, so-called matrix type display devices, the resolution of the picture image is determined by the size and pitch of the holes provided in the electron beam control electrodes or their substrates. Accordingly, the higher the resolution of the picture image, and thus the clearer the picture image it is desired to achieve, the smaller the diameter of the holes and the pitch. Accordingly, in order to obtain a clear picture image on a display screen of a particular size, the holes 6a and 6b and the group of electrodes 7 and 8 need to be closely arranged, and accordingly, the number of holes and the number of electrodes must be greatly increased. For example, for the purpose of displaying a TV picture image, a minimum of 500.times.500 holes are required, and for each electron beam control electrode plate, 500 electrodes are needed. If a color display is desired, three times this number of holes and electrodes are necessary.
The number of such electrodes that can be accommodated in view of the materials and the manufacturing techniques available at the present present time is limited to 2-3 per 1 mm of space, thus making it difficult to obtain the proper resolution. Moreover, as the numbers of holes and electrodes are increased, the driving circuits and the junctions between the driving circuits and respective electrodes greatly increase in number, posing a grave problem of actual installation, or giving rise to failures in the device. Such difficult problems are many.